1. Field of the Invention
The present invention relates to radio communication apparatuses with wireless communication functions, and it particularly relates to a communication terminal apparatus equipped with a plurality of communication modules.
2. Description of the Related Art
In recent years, a variety of wireless communication protocols have been proposed and put to practical use. Representative of such protocol technologies are the widedband wireless local area network system (WLAN) standardized by the IEEE 802.11 and the wireless communication technology for mobile information devices □e.g., Bluetooth: registered trademarks□ standardized by the IEEE802.15.1. Incorporated into diverse information terminal apparatuses, such technologies are used in wireless connection with peripheral devices, such as PDAs (personal digital assistants), printers and headsets. Owing to the technological innovation of recent years, wireless communication modules today are manufactured small and inexpensive, and it is also possible to build modules employing multiple types of wireless communication protocols into a single device or casing.
A wireless communication module must be able to transmit signals for a certain distance, receive weak radio waves transmitted by a peripheral device and reproduce signals therefrom. Accordingly, a wireless communication module is structured by a transmitter capable of high output and a receiver with high sensitivity.
If a plurality of wireless communication modules are built into a single device or casing, those wireless communication modules will be placed in close proximity to one another because of the limited space. As a natural consequence, mutual interference of radio waves occurs among the wireless communication modules themselves. In particular, the problem of mutual interference can be pronounced between a wireless communication protocol defined by the IEEE 802.11 (hereinafter referred to as “WLAN” or “WLAN protocol”) and a wireless communication protocol defined by the IEEE 802.15.1 (hereinafter referred to as “Bluetooth” or “Bluetooth protocol”), both of which use the same 2.4 GHz band.
A technology developed for the Bluetooth protocol to avoid interference among different wireless communication modules is called AFH (Adaptive Frequency Hopping). The AFH technology stabilizes communication under the Bluetooth protocols by frequency hopping, in which a Bluetooth communication module avoids the use of the frequency bands occupied by the other communication modules in the same range of frequency and uses only usable frequencies for communication.
However, when a plurality of wireless communication modules are built into a single device or casing, those wireless communication modules must be placed in close proximity to one another. Thus, the countermeasure by AFH alone cannot sufficiently eliminate the mutual interference of radio waves therebetween. Especially when a wireless communication module is in a transmission mode and at the same time another adjacent wireless communication module is in a reception mode, the latter cannot avoid receiving the high-output transmission waves outputted by the former in close vicinity. Consequently, the signals to be received primarily may get buried in the received radio waves, thus creating a situation where necessary signals cannot be reproduced properly. Therefore, it is strongly desired that a technology be developed that can realize a stable communication when a plurality of wireless communication modules are built into a single device or casing.